1. Field of the Invention
The present invention relates to a spindle motor and a hard disk drive including the same.
2. Description of the Related Art
Generally, a small spindle motor used in a hard disk drive (HDD) serves to rotate a disk so that a magnetic head can write data to the disk or read data from the disk.
In addition, the spindle motor is provided with a hydrodynamic bearing assembly, and a bearing clearance formed in the hydrodynamic bearing assembly is filled with a lubricating fluid.
In addition, at the time of rotation of a shaft, the lubricating fluid in the bearing clearance is pumped to form fluid dynamic pressure therein, thereby rotatably supporting the shaft.
However, pressure lower than atmospheric pressure, that is, negative pressure, may be generated in the bearing clearance due to the pumping of the lubricating fluid at the time of rotation of the shaft.
In this case, air contained in the lubricating fluid expands, such that air bubbles are formed. When such air bubbles are introduced into a groove pumping the lubricating fluid, deterioration of rotational characteristics such as the generation of insufficient fluid dynamic pressure, the generation of vibrations, and the like, may occur.
Therefore, a circulation hole for decreasing the generation of negative pressure is formed in a sleeve to suppress the generation of negative pressure.
In the following Related Art Document (US 2009-0080819), a configuration in which a circulation hole for decreasing the generation of negative pressure is formed to be inclined and connects a bearing clearance formed by a sleeve and a cover member and a bearing clearance in which a liquid-vapor interface is formed to each other has been used.
However, it may be difficult to process the circulation hole and a defect may occur in the sleeve at the time of processing the circulation hole.